#include <iostream>
using namespace std;
int main()
{
    long long a[51],n,i;
    a[1]=1;a[2]=2;
    for (i=3;i<=50;i++)a[i]=a[i-1]+a[i-2];
    while (cin>>n)
    {
        cout<<a[n]<<endl;
    }
    return 0;
}
